The proposed studies will further investigate the function of quiescent leukemic cells in non B - non T acute lymphoblastic leukemia in children and will develop means of recruiting them into the cell cycle. Multivariate analysis of DNS/RNA flow cytometric and clinical data has identified quiescent cells with low RNA content as resistant to early induction therapy. Correlation of WBC and cell kinetics showed that high WBC is associated with low RNA content (quiescence) of bone marrow blasts. These "G0-" cells will be further analyzed by multiparameter flow cytometric investigations of the nuclear antigens K167 and PCNA ("Cyclin") of chromatin structure in-situ and of a novel proliferation-related cell surface antigen (A18). The nuclear protein of the proto- oncogene p53 will be further studied by immunoprecipitation. P53 expression is cell cycle dependent and our preliminary data indicate that patients with high p53 expression have poor prognosis. A small population of aneuploid leukemic cells with restricted cell surface light chain expression has been identified in untreated patients. These cells appear to be quiescent and their relationship to the "G0" population will be further investigated in conjunction with the above proliferation markers. FACS-sorting of cells has identified these cells as having morphological features of more mature lymphocytes, consistent with the notion that a subpopulation of leukemic cells differentiates in-vivo. We will study the co-expression of these cells of light chains and of the CD19 antigen and then investigate if differentiated and/or quiescent cell can be diminished by an anti- CD19-ricin immunotoxin. The expression of the p-glycoprotein on proliferating, quiescent and differentiated leukemic cells will be studied using an novel antibody directed against a surface epitope of gp180. In-vitro studies have demonstrated the possibility of recruitment of leukemic cells from G0 to G1 by IL-2/OKT-3/PMA. BCGF and IL-6 will be studied in their ability to recruit aneuploid leukemic cells into the cell cycle and subsequent treatment with daunomycin, ARA-C and MTX will test the hypothesis that recruited cells have increased sensitivity to cytotoxic chemotherapy. If successful, these studies will introduce cytokines into chemotherapeutic regimen for the treatment of pediatric All and will hopefully improve the remission duration for children with poor risk and relapsed ALL.